Accurate tracking of targets (e.g. radar tracking of airborne targets) among multiple floating platforms or vessels at sea, as well as sharing tracking data among multiple floating platforms and land-based systems, requires increasingly advanced technical innovations to provide corrections to internal ship flexure and relative earth coordinates. Positioning systems according to the prior art typically attempt to acquire satellite tracking data over a period of hours, determine errors, and apply appropriate corrections. However, these processes ignore any shifts in static flexure or any current dynamic flexure errors of the platforms or vessels being tracked. These types of bias changes may be the result of many factors, including temperature distortions (e.g. from the sun), which can be observed in a matter of minutes after maneuvering a ship, or in mere seconds in the case of dynamic flexure events. Accordingly, hours of data acquisition would be insufficient to accomplish an accurate correction solution without some additional augmentation. Moreover, these systems inherently introduce errors as a result of inaccuracies in their measuring devices.
Referring generally to FIG. 1, there is shown an exaggerated illustration of the above-described errors induced by current GPS-based positioning systems employed on vessels 100,101,102. These errors include, for example, deviations in perceived True North and actual True North bearings, as well as deviations in perceived location versus an actual or true location. In addition, a ship can distort such that one structural section can be out of phase in roll, pitch or yaw with respect to another structural section. The errors may create significant performance reductions when affected position data is utilized by on-ship systems. For example, a ship's on-board radar system may magnify these errors when attempting to track distant airborne targets. Further still, these inaccuracies may result in increased difficulties performing operations among multiple ships. By way of example, exchanging radar tracking or track data of an airborne target between multiple platforms may be detrimentally affected by the discrepancies between the relative reference positions of each platform and its influence on a perceived measured flight path. This may result in the creation of one or more sets of phantom tracks in gridlocking processes resulting from these discrepancies.
As will be understood by one of ordinary skill in the art, the term gridlocking is generally used to describe a process of receiving track data from multiple source locations and correlating jointly held targets to build a composite track, larger in volume compared to that achievable by a single source. One issue is that track data from multiple sensors on one platform can have time varying biases from each sensor, but gridlocking techniques apply a single correction for data from one platform. This can create multiples of a single target or even delete a valid target from consideration in the composite track picture.
Alternative systems and methods to determine local flexure corrections, roll and pitch values, as well as for determining relative True North for use by multiple platforms are desired.